Fluorophosphate glasses for active device

ABSTRACT

The disclosed fluorophosphate glasses for an active device include: a metaphosphate composition including Al(PO3)3; a fluoride composition including BaF2 and SrF2; and a dopant composed of ErF3 and YbF3, and have thermal and mechanical properties to be able to be used as a glass base material for an active device (e.g., optical fiber laser), have a high emission cross-section characteristic, have a reinforced upconversion and downconversion emission characteristic, and have high sensitivity S in a cryogenic environment.

FIELD

The present disclosure relates to fluorophosphate glasses for an activedevice and, more particularly, to the composition of fluorophosphateglasses for an active device, the fluorophosphate glasses having thermaland mechanical properties to be able to be used as a glass base materialfor an optical fiber laser, having a high emission cross-sectioncharacteristic, having a reinforced upconversion and downconversionemission characteristic, and having high sensitiveness S in a cryogenicenvironment.

BACKGROUND

This section provides background information related to the presentdisclosure which is not necessarily prior art.

In general, an erbium-doped fiber amplifier (EDFA), which is an opticalfiber amplifier device that is used as an important device in not only awavelength division multiplexing (WDM) communication system, but mostoptical networks, amplifies light having a wavelength between 1530 and1610 nm by doping an optical fiber made of glass with erbium.

Fluorophosphate (FP) glass produced by mixing fluoride glass withphosphate has excellent thermal stability and chemical durability, lowphonon energy, and excellent linearity of a light transmittancecharacteristic and a refractive index in a wide spectrum region from theultraviolet ray to the near infrared ray, as compared with fluorideglass. Further, when a rare earth (RE) element is used as a dopant, highdopant concentration can be achieved by providing multiple energylevels, so the fluorophosphate glass is a glass base material that canachieve high efficiency even using a short cavity.

Meanwhile, ytterbium (Yb) provides a considerably high absorption crosssection in the region of 980 nm, and is used as a sensitizer of laserexcitation by being co-doped with erbium (Er) because overlap of theenergy level of a donor (²F_(5/2), Yb³⁺) and the energy level of anacceptor (⁴I_(11/2), Er³⁺).

The application range of the fluorophosphate glass co-doped with Er/Ybhaving these excellent characteristics, in order to use the excellentcharacteristics described above, has been increased recently up to notonly existing applications such as a visible light or infrared laser, anoptical fiber amplifier, an optical storage device, and a submarineoptical communication network, but a 3D space observation system thatrequires high output, an eye-safe light source (1550 nm), and lightweight such as LiDAR (Light Detection and Ranging).

Further, a green color having a wavelength of 500 nm band and a redcolor having a wavelength of 600 nm band are used in fields such as abiotechnology and data storage.

In order to be used in this wide application field, it is required todevelop a fluorophosphate glass base material that can achieve highpulse output even if the size of a device is reduced. Further, it isrequired to use an upconversion phenomenon in order to emit a wavelengthof 500 to 600 nm using a laser excitation system of 980 nm.

SUMMARY Technical Problem

An object of the present disclosure is to provide fluorophosphateglasses for an active device, the fluorophosphate glasses having thermaland mechanical properties to be able to be used as a glass base materialfor an active device (e.g., an optical fiber laser), having a highemission cross-section characteristic, having a reinforced upconversionand downconversion emission characteristic, and having high sensitivityS in a cryogenic environment.

Technical Solution

This section provides a general summary of the disclosure and is not acomprehensive disclosure of its full scope or all of its features.

In order to achieve the objects, fluorophosphate glasses for an activedevice according to an aspect of the present disclosure includes: ametaphosphate composition including Al(PO₃)₃; a fluoride compositionincluding BaF₂ and SrF₂; and a dopant composed of ErF₃ and YbF₃.

In the fluorophosphate glasses for an active device according to anaspect of the present disclosure, the YbF₃ may be about 3 mol % to about5 mol %.

In the fluorophosphate glasses for an active device according to anaspect of the present disclosure, the ErF₃ may be about 3 mol % and YbF₃may be about 3 mol % to about 5 mol %.

In the fluorophosphate glasses for an active device according to anaspect of the present disclosure, the Al(PO₃)₃ may be about 20 mol % toabout 30 mol %, the BaF₂ may be about 10 mol % to about 60 mol %, andthe SrF₂ may be about 10 mol % to about 70 mol %.

In the fluorophosphate glasses for an active device according to anaspect of the present disclosure, the Al(PO₃)₃ may be about 20 mol %,the BaF₂ may be about 40 mol % to about 60 mol %, and the SrF₂ may beabout 20 mol % to about 40 mol %.

In the fluorophosphate glasses for an active device according to anaspect of the present disclosure, the ErF₃ may be about 3 mol % and YbF₃may be about 3 mol % to about 5 mol %.

In the fluorophosphate glasses for an active device according to anaspect of the present disclosure, the Al(PO₃)₃ may be about 20 mol %,the BaF₂ may be about 60 mol %, and the SrF₂ may be about 20 mol %.

In the fluorophosphate glasses for an active device according to anaspect of the present disclosure, the ErF₃ may be about 3 mol % and YbF₃may be about 3 mol % to about 5 mol %.

In the fluorophosphate glasses for an active device according to anaspect of the present disclosure, the Al(PO₃)₃ may be about 20 mol %,the BaF₂ may be about 50 mol %, and the SrF₂ may be about 30 mol %.

In the fluorophosphate glasses for an active device according to anaspect of the present disclosure, the ErF₃ may be about 3 mol % and YbF₃may be about 3 mol % to about 5 mol %.

In the fluorophosphate glasses for an active device according to anaspect of the present disclosure, the Al(PO₃)₃ may be about 20 mol %,the BaF₂ may be about 40 mol %, and the SrF₂ may be about 40 mol %.

Advantageous Effects

According to the present disclosure, thermal properties including glasstransition temperature (tg) and peak temperature (tp), thermomechanicalproperties including coefficient of thermal expansion (CTE), andmechanical properties including Knop hardness are improved, so there isprovided an advantage in the process of manufacturing an active deviceincluding an optical fiber laser.

According to the present disclosure, there is an effect of being able toachieve high pulse output even if the size of a device decreases byachieving a high emission cross-section characteristic.

According to the present disclosure, there is an effect of increasingthe lifetime of carriers at a metastable state energy level that isstimulated-emitted due to an effective energy transfer phenomenon by thecomposition optimization of dopants (e.g., Er and Yb).

According to the present disclosure, there is an effect of reinforcingdownconversion and upconversion emission characteristics by thecomposition optimization of dopants (e.g., Er and Yb).

According to the present disclosure, it is possible to obtain a glassbase material for an active device which has excellent sensitivity atcryogenic temperature. Therefore, it is possible to provide an activedevice that can be used in a cryogenic environment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B, and 1C are diagrams of glass composition design ofAl(PO₃)₃—BaF₂—(Sr, Ca, Mg)F₂.

FIGS. 2A, 2B, and 2C are diagrams showing test results of thermalproperty estimation of Al(PO₃)₃—BaF₂—(Sr, Ca, Mg)F₂.

FIGS. 3A, 3B, and 3C are diagrams showing test results of thermalproperty estimation of ErF₃—Al(PO₃)₃—BaF₂—(Sr, Ca, Mg)F₂.

FIG. 4 is a diagram showing a test result of thermomechanical propertyestimation according to a composition change of Al(PO₃)₃—BaF₂—(Sr, Ca,Mg)F₂.

FIGS. 5A, 5B, and 5C are diagrams showing test results of mechanicalproperty estimation according to glass composition design ofAl(PO₃)₃—BaF₂—(Sr, Ca, Mg)F₂.

FIGS. 6A, 6B, and 6C are diagrams showing test results of mechanicalproperty estimation according to glass composition design ofErF₃—Al(PO₃)₃—BaF₂—(Sr, Ca, Mg)F₂.

FIG. 7 is a diagram showing an absorption spectrum according toytterbium (Yb) concentration ofAl(PO₃)₃-(40−x)BaF₂—SrF₂-(0.03)ErF₃/(x)YbF₃-based glass (x=0.03:ASB3E3Y,0.04:ASB3E4Y, 0.05:ASB3E5Y).

FIG. 8 is a diagram showing a change of Judd-Ofelt parameters accordingto ytterbium (Yb) concentration ofAl(PO₃)₃-(40−x)BaF₂—SrF₂-(0.03)ErF₃/(x)YbF₃-based glass.

FIG. 9 is a diagram showing an upconversion spectrum according toytterbium (Yb) concentration ofAl(PO₃)₃-(40−x)BaF₂—SrF₂-(0.03)ErF₃/(x)YbF₃-based glass (x=0.01, 0.02,0.03, 0.04, 0.05).

FIG. 10 is a diagram showing a near infrared ray emission spectrumaccording to ytterbium (Yb) concentration ofAl(PO₃)₃-(40−x)BaF₂—SrF₂-(0.03)ErF₃/(x)YbF₃-based glass (x=0.01, 0.02,0.03, 0.04, 0.05).

FIG. 11 is a diagram showing a test result of an absorptioncross-section (ACS) and an emission cross-section (ECS) of⁴I_(13/2)→⁴I_(15/2) conversion according to the wavelength ofAl(PO₃)₃—(40−x)BaF₂−SrF₂-(0.03)ErF₃/(x)YbF₃-based glass (x=0.04).

FIG. 12 is a diagram showing a test result of a gain constant changeaccording to the wavelength and the population inversion ratio ofAl(PO₃)₃-(40−x)BaF₂—SrF₂-(0.03)ErF₃/(x)YbF₃-based glass (x=0.04).

FIG. 13 is a diagram showing a carrier attenuation curve at an energylevel of ⁴I_(13/2) according to ytterbium (Yb) concentration ofAl(PO₃)₃-(40−x)BaF₂—SrF₂-(0.03)ErF₃/(x)YbF₃-based glass (x=0.01, 0.02,0.03, 0.04, 0.05).

FIG. 14A is a diagram showing a test result of a carrier emissioncross-section change according to ytterbium (Yb) concentration in asample composition 8 of Al(PO₃)₃-(1−x)BaF₂—SrF₂-(0.03)ErF₃/(x)YbF₃-basedglass (x=0.01, 0.02, 0.03, 0.04, 0.05).

FIG. 14B is a diagram showing a test result on a carrier emissioncross-section change according to ytterbium (Yb) concentration in asample composition 9 of Al(PO₃)₃-(1−x)BaF₂—SrF₂-(0.03)ErF₃/(x)YbF₃-basedglass (x=0.01, 0.02, 0.03, 0.04, 0.05).

FIG. 14C is a diagram showing a test result on a carrier emissioncross-section change according to ytterbium (Yb) concentration in asample composition 10 ofAl(PO₃)₃-(1−x)BaF₂—SrF₂-(0.03)ErF₃/(x)YbF₃-based glass (x=0.01, 0.02,0.03, 0.04, 0.05).

FIG. 15A is an energy level diagram illustrating a photon emissionphenomenon according to absorption and downconversion of photons in anEr/Yb system.

FIG. 15B is an energy level diagram illustrating a photon emissionphenomenon according to absorption and upconversion of photons in anEr/Yb system.

FIG. 16 is a diagram illustrating a low-temperature upconversionemission spectrum of Al(PO₃)₃-(1−x)BaF₂—SrF₂-(0.03)ErF₃/(x)YbF₃-basedglass (x=0.05).

FIG. 17A is a diagram illustrating a fluorescence intensity ratio (FIB)of green emissions of Al(PO₃)₃-(1−x)BaF₂—SrF₂-(0.03)ErF₃/(x)YbF₃-basedglass (x=0.05).

FIG. 17B is a diagram illustrating a change according to temperature ofsensitivity S of glass of FIG. 17A.

DETAILED DESCRIPTION

Hereafter, embodiments of achieving fluorophosphate glasses for anactive device according to the present disclosure are described indetail with reference to the drawings.

However, it should be understood that the spirit of the presentdisclosure is not considered as being limited to the embodimentsdescribed below and those skilled in the art may easily propose variousembodiments included in the same spirit as the present disclosurethrough changing and modifying, but the changes and modification areincluded in the spirit of the present disclosure.

Further, the terms to be used hereafter are selected for the convenienceof description and should be appropriately construed as meaningscoinciding with the spirit of the present disclosure, not being limitedto the meanings in dictionaries when finding out the spirit of thepresent disclosure.

Fluorophosphate glasses according to the present embodiment haveAl(PO₃)₃—BaF₂—(Sr, Ca, Mg)F₂ as a base material. In detail, theinventor(s) proposes the composition of fluorophosphate glasses composedof ErF₃—YbF₃—Al(PO₃)₃—BaF₂—SrF₂ or has these compositions as a basematerial as characteristic of the present disclosure.

Accordingly, as for Al(PO₃)₃—BaF₂—(Sr, Ca, Mg)F₂-based glass, bysatisfying thermal and mechanical property conditions that can beapplied to glass for an active device (e.g., an optical fiber laser) andoptimizing the composition ratio (mol %) of a dopant composed of Er³⁺and Yb³⁺, a high emission cross-section characteristic is achieved suchthat an effect that can achieve high pulse output even if the size ofdevices is reduced can be derived.

FIGS. 1A, 1B, and 1C are diagrams of glass composition design ofAl(PO₃)₃—BaF₂—(Sr, Ca, Mg)F₂.

Referring to FIGS. 1A, 1B, and 1C, it can be seen that a samplecomposition determined on the basis of a glass forming region in amaterial combination of fluorophosphate glasses that uses Al(PO₃)₃ asphosphate and is used as each of a fluorine compound of strontium (Sr),calcium (Ca), and magnesium (Mg).

In FIGS. 1A, 1B, and 1C, it is the sample composition positioned in ablack boundary (closed curve) and suitability as a glass base materialfor an active device is checked by analyzing thermal and mechanicalproperty changes according to a change of the composition ratio (mol %)of each composition.

FIGS. 2A, 2B, and 2C are diagrams showing test results of thermalproperty estimation of Al(PO₃)₃—BaF₂—(Sr, Ca, Mg)F₂ and FIGS. 3A, 3B,and 3C are diagrams showing test results of thermal property estimationof ErF₃—Al(PO₃)₃—BaF₂—(Sr, Ca, Mg)F₂.

An optical fiber is manufactured by reheating and drawing a glass basematerial manufactured in an ingot shape at predetermined temperature andat a predetermined speed.

Accordingly, glass transition temperature Tg and peak temperature Tp areimportant factors that determine difficulty and yield of a process ofglass base materials for manufacturing optical fibers.

Referring to FIGS. 2A, 2B, and 2C, it can be seen inAl(PO₃)₃—BaF₂—MgF₂-base glass, as the content of MgF₂ increases insteadof BaF₂, the change of the glass transition temperature Tg is not largeand it can be also seen in Al(PO₃)₃—BaF₂—CaF₂-based glass, as thecontent of CaF₂ increases instead of BaF₂ from the sample composition 6to the sample composition 7, there is little change in the glasstransmission temperature Tg.

Further, as the content of SrF₂ increases from 0.2 mol % to 0.7 mol %instead of BaF₂ from the sample composition 8 to the sample composition14 in a Al(PO₃)₃—BaF₂—SrF₂-based glass composition candidate, there isno thermal property displacement behavior tendency, so it is determinedas relatively slight.

Accordingly, in Al(PO₃)₃—BaF₂—(Sr, Ca, Mg)F₂-based glass, a change inthe composition has low influence on the difficulty and yield of adrawing process in manufacturing of an optical fiber, so there is theadvantage that the composition optimization for adjusting othercharacteristics is possible.

Meanwhile, it can be seen that the content of Al(PO₃)₃ that is a networkformer increases from 0.2 mol % to 0.3 mol %, the structure of rigidityrelatively increases and the glass transition temperature increases, sothere is a limit in a composition change range of the content ofAl(PO₃)₃.

Referring to FIGS. 3A, 3B, and 3C, it can be seen that as ErF₃ increasesin ErF₃—Al(PO₃)₃—BaF₂—MgF₂-based glass of (0.01, 0.02) mol %, the glasstransition temperature linearly decreases and the same tendency can bealso seen in ErF₃—Al(PO₃)₃—BaF₂—CaF₂-based glass of (0.01, 0.02) mol %and ErF₃—Al(PO₃)₃—BaF₂—SrF₂-based glass of (0.01, 0.02) mol %.

In general, when rare earth ions are added, a phenomenon that isopposite to the phenomenon that glass transition temperature relativelyincreases is shown.

Further, it is shown that as ErF₃ increases inErF₃—Al(PO₃)₃—BaF₂—MgF₂-based glass of (0.01, 0.02) mol %, the glasstransition temperature linearly decreases and it can be seen that thesame tendency can be also seen in ErF₃—Al(PO₃)₃—BaF₂—CaF₂-based glass of(0.01, 0.02) mol % and ErF₃—Al(PO₃)₃—BaF₂—SrF₂-based glass of (0.01,0.02) mol %.

FIG. 4 is a view showing a test result of thermal, mechanical propertyestimation according to a composition change of ErF₃-dopedAl(PO₃)₃—BaF₂—(Sr, Ca, Mg)F₂.

When an optical fiber expands or contracts in accordance with externaltemperature, the transmission characteristic of a communication systemis obviously deteriorated and a change of a gain characteristic iscaused in an optical fiber laser or an optical fiber amplifier, so it ispreferable that a coefficient of thermal expansion is small.

Referring to FIG. 4, as for the coefficient of thermal expansion (CTE)by Er³⁺ doping, the change tendency of the coefficient of thermalexpansion according to the amount of Er³⁺ doping inAl(PO₃)₃—BaF₂—MgF₂-based glass and Al(PO₃)₃—BaF₂—CaF₂-based glass isalso similarly shown in Al(PO₃)₃—BaF₂—SrF₂-based glass. Accordingly, itcan be found out that when the Al(PO₃)₃—BaF₂—SrF₂-based glass is appliedto an optical fiber laser or an optical fiber amplifier, acharacteristic that is advantageous for interfacial bonding of a coreand a cladding would be obtained.

FIGS. 5A, 5B, and 5C are diagrams showing test results of mechanicalproperty estimation according to glass composition design ofAl(PO₃)₃—BaF₂—(Sr, Ca, Mg)F₂ and FIGS. 6A, 6B, and 6C are diagramsshowing test results of mechanical properties according to glasscomposition design of ErF₃—Al(PO₃)₃—BaF₂—(Sr, Ca, Mg)F₂.

Referring to FIGS. 5A, 5B, and 5C, it can be seen that as the BaF₂ mol %decreases from 0.7 to 0.3, that is, MgF₂ mol % increases from 0.2 to 0.5in 0.2Al(PO₃)₃, the hardness of the Al(PO₃)₃—BaF₂—MgF₂-based glasslinearly increases.

Meanwhile, the hardness is relatively low in the sample composition 4,which is determined because the composition ratio of Al(PO₃)₃ decreasedto 0.1.

Accordingly, it can be seen that as the composition ratio of Al(PO₃)₃increases in the Al(PO₃)₃—BaF₂—MgF₂-based glass, the hardness linearlyincreases.

Next, as for a hardness change of the Al(PO₃)₃—BaF₂—CaF₂-based glass, itcan be seen that as BaF₂ mol % decreases from 0.7 to 0.4, that is, CaF₂mol % increases from 0.1 to 0.4 in 0.2Al(PO₃)₃, the hardness linearlyincreases and the same hardness increase is shown in 0.3Al(PO₃)₃.

Further, when Al(PO₃)₃ increases, the hardness relatively increases, soit can be seen in this test that when the composition changes from thenumber 6 to the number 14, the hardness also linearly increases.

Next, as for a hardness change of Al(PO₃)₃—BaF₂—SrF₂-based glass, first,when the BaF₂ composition mole ratio is relatively large as 0.6 mol %,as in the composition samples 8 and 14, the hardness is very small.

In particular, it could be seen that there is little influence eventhough mol % of Al(PO₃)₃ increases in the Al(PO₃)₃—BaF₂—SrF₂-basedglass.

Meanwhile, as SrF₂ mol % increases from 0.4 to 0.7, that is, from thecomposition 9 to composition 13 with 0.2Al(PO₃)₃ fixed, the hardnesslinearly increases, which means that, according to the change tendencyof hardness of Al(PO₃)₃—BaF₂—(Ca, Mg, Sr)F₂ fluorophosphate glass, thehardness is small in the region with a large composition ratio of BaF₂and the hardness generally increases with an increase in CaF₂, MgF₂, orSrF₂ composition ratio to BaF₂. Further, an increase of phosphate withhigh melting temperature results in improvement of hardness.

Meanwhile, referring to FIGS. 6A, 6B, and 6C, it can be seen as (0.01,0.02) mol % ErF₃ is added to Al(PO₃)₃—BaF₂—(Mg, Ca, Sr)F₂-based glass,Knoop hardness linearly increases.

When it is added up to 0.01 mol % ErF₃ concentration, as a test, it isexpected that ligand and covalent bonding around Er ions increase, so,relatively, the glass transition temperature increases and hardness isimproved when rare earth ions are relatively added even in considerationof non-uniform distribution of Er³⁺ ions in glass crystals due tovolatility.

FIG. 7 is a diagram showing an absorption spectrum according toytterbium (Yb) concentration ofAl(PO₃)₃-(40−x)BaF₂—SrF₂-(0.03)ErF₃/(x)YbF₃-based glass (x=0.03:ASB3E3Y,0.04:ASB3E4Y, 0.05:ASB3E5Y).

Referring to FIG. 7, as YbF₃ increases from 3 mol % to 5 mol %,transition intensity of ²F_(7/2)→2F_(5/2) keeps increasing. Thetransition intensity of ⁴I_(15/2)→⁴I_(13/2) increases and thensaturates, as YbF₃ increases. Further, the decreased intensity of⁴I_(13/2) and the energy level excited from the intensity show thatthere is an upconversion phenomenon.

Meanwhile, the absorption spectrum of FIG. 7 is applied to Judd-OfeltTheory to calculate oscillation strengths, an intensity parameter,spontaneous emission probabilities, a branching ratio, and a radiativelifetime.

FIG. 8 is a diagram showing a Judd-Ofelt parameter change according toytterbium (Yb) concentration ofAl(PO₃)₃-(40−x)BaF₂—SrF₂-(0.03)ErF₃/(x)YbF₃-based glass (x=0.03:ASB3E3Y,0.04:ASB3E4Y, 0.05:ASB3E5Y).

Referring to FIG. 8, it can be seen through Judd-Ofelt analysis that asYbF₃ increases, the Judd-Ofelt parameter Ω_(λ) keeps increasing. Thismeans that as YbF₃ increases, the average symmetry of Er³⁺ ionsdecreases and the covalency of Er—O bonding increases. Accordingly, aperformance indicator that is about 2.04-time higher is obtained forX=0.05, as compared with the related art, so there is a high possibilityof being able to be used as a laser gain medium for X=0.05.

FIG. 9 is a diagram showing an upconversion spectrum according toytterbium (Yb) concentration ofAl(PO₃)₃-(40−x)BaF₂—SrF₂-(0.03)ErF₃/(x)YbF₃-based glass (x=0.01, 0.02,0.03, 0.04, 0.05).

Referring to FIG. 9, two strong green emission peaks are shown 525 nm(²H_(11/2)→⁴I_(15/2)) and 545 nm (⁴S_(3/2)→⁴I_(15/2)) and one weak redemission peak is shown at 651 nm (⁴F_(9/2)→⁴I_(15/2)). That is, it canbe seen that as the concentration of YbF₃ increases, the intensities ofthe green emission and the red emission monotonously increase.

FIG. 10 is a diagram showing a near infrared ray emission spectrumaccording to ytterbium (Yb) concentration ofAl(PO₃)₃-(40−x)BaF₂—SrF₂-(0.03)ErF₃/(x)YbF₃-based glass (x=0.01, 0.02,0.03, 0.04, 0.05).

Referring to FIG. 10, it can be seen that an emission phenomenon of awavelength of 1540 nm is a characteristic band of internal-4f conversionbetween ⁴I_(15/2) and ⁴I_(13/2) manifolds for excited Er³⁺ ions having awide band. That is, as YbF₃ increases from 1.0 mol % to 3.0 mol %,emission intensity of a wavelength of 1540 nm increases, so when theYbF₃ concentration increases over 3.0 mol %, the emission intensity ofthe wavelength of 1540 nm decreases.

Further, a full width at half maximum (FWHM) increases from 67 nm to 78nm when YbF₃ increases from 1.0 mol % to 4.0 mol % and decreases whenthe YbF₃ concentration is 5.0 mol %. When the YbF₃ concentration is 5.0mol %, the emission intensity and FWHM are decreased by a non-radiativeprocess due to cluster formation.

FIG. 11 is a diagram showing a test result of an absorptioncross-section (ACS) and an emission cross-section (ECS) of⁴I_(13/2)→⁴I_(15/2) conversion according to the wavelength ofAl(PO₃)₃-(40−x)BaF₂—SrF₂-(0.03)ErF₃/(x)YbF₃-based glass (x=0.04).

Referring to FIG. 11, as the YbF₃ concentration increases, theabsorption cross-section and the emission cross-section decrease.However, when YbF₃ is 4.0 mol %, the absorption cross-section and theemission cross-section increase due to an appropriate Er/Ybconcentration ratio that may induce effective resonant energy transferfrom Yb³⁺ to Er³⁺.

FIG. 12 is a diagram showing a test result of a gain constant changeaccording to the wavelength and the population inversion ratio ofAl(PO₃)₃-(40−x)BaF₂—SrF₂-(0.03)ErF₃/(x)YbF₃-based glass (x=0.04).

Referring to FIG. 12, it can be seen that when the population inversionratio γ is 0.4 or more, the gain constant at 1540 nm may have a positivevalue. From this phenomenon, it can be seen that a low pump thresholdvalue is required to laser operation of ⁴I_(13/2)→⁴I_(15/2) transition.

When the population inversion ratio γ is 0.4 or more, the laser emissionwavelength moves to a short wavelength. Further, when the populationinversion ratio γ is 0.4 or more, the bandwidth is 74 nm, which is verywide in comparison to the bandwidth of a common silicated erbium-dopedfiber amplifier.

When population inversion ratio γ is 0.4 or more, a flat gaincharacteristic is shown in the range of 1490 nm to 1620 nm includingC(1530-1565 nm) and L(1565-1625 nm) bands of an optical communicationwindow. Accordingly, it is possible to receive more channels inwavelength division multiplex networks.

FIG. 13 is a diagram showing a carrier attenuation curve at an energylevel of ⁴I_(13/2) according to ytterbium (Yb) concentration ofAl(PO₃)₃-(40−x)BaF₂—SrF₂-(0.03)ErF₃/(x)YbF₃-based glass (x=0.01, 0.02,0.03, 0.04, 0.05).

Referring to FIG. 13, when the concentration of YbF₃ increases from 1.0mol % to 5.0 mol %, the carrier lifetime τ_(exp) at an energy level of⁴I_(13/2) is determined as 8.73, 11.85, 11.55, 12.37, and 10.47 ms. Asthe concentration of YbF₃ increases from 1.0 mol % to 4.0 mol %, τ_(exp)increases from 8.73 ms to 12.37 ms, and when concentration of YbF₃increases to 5.0 mol %, τ_(exp) decreases to 10.47 ms.

The increase of τ_(exp) with an increase from 1.0 mol % to 4.0 mol % ofthe concentration of YbF₃ is because excitation through energyconversion according to the increase in concentration of YbF₃ anddispersion by ErF₃ increase. Further, the decrease of τ_(exp) due to theincrease to 5.0 mol % of the concentration of YbF₃ is because anon-radiative loss is increased due to cluster formation. Accordingly,τ_(exp) when x is 0.02 to 0.05 inAl(PO₃)₃-(40−x)BaF₂—SrF₂-(0.03)ErF₃/(x)YbF₃ is longer than that offluorophosphate glasses or fluorophosphate glasses based on Al(PO₃)₃ inthe related art.

Next, an emission cross-section characteristic of fluorophosphateglasses for an active device according to the present embodiment isdescribed.

FIGS. 14A to 14C are diagrams showing test results of a carrier emissioncross-section change according to ytterbium (Yb) concentration in samplecompositions 8, 9, and 10 ofAl(PO₃)₃-(1−x)BaF₂—SrF₂-(0.03)ErF₃/(x)YbF₃-based glass (x=0.01, 0.02,0.03, 0.04, 0.05).

Referring to FIG. 14A, it can be seen that the emission cross-section isthe highest as 4.841×10⁻²¹ cm² at (0.03)ErF₃/(0.05)YbF₃ for a triaxialcomposition 8 (referred to as ‘ABS-8’) ofAl(PO₃)₃-(1−x)BaF₂—SrF₂-(0.03)ErF₃/(x)YbF₃-based glass (x=0.01, 0.02,0.03, 0.04, 0.05).

Referring to FIG. 14B, it can be seen that the emission cross-section isthe highest as 4.2412×10⁻²¹ cm² at (0.03)ErF₃/(0.04)YbF₃ for a triaxialcomposition 9 (referred to as ‘ABS-9’) ofAl(PO₃)₃-(1−x)BaF₂—SrF₂-(0.03)ErF₃/(x)YbF₃-based glass (x=0.01, 0.02,0.03, 0.04, 0.05).

Referring to FIG. 14C, it can be seen that the emission cross-section isthe highest as 4.145×10⁻²¹ cm² at (0.03)ErF₃/(0.03)YbF₃ for a triaxialcomposition 10 (referred to as ‘ABS-10’) ofAl(PO₃)₃-(1−x)BaF₂—SrF₂-(0.03)ErF₃/(x)YbF₃-based glass (x=0.01, 0.02,0.03, 0.04, 0.05).

In other words, these results are considered as being caused by arelatively small ratio of quenching effect, such as energy transitionand multiphonon relaxation of rare earth elements.

Further, when the content of SrF₂ increases instead of BaF₂ with acomposition change of a base material, that is, the sample compositionincreases from sample composition ABS-8 to sample composition ABS-10,the relatively highest emission cross-section is shown at the ratio ofErF₃:YbF₃=0.03:0.03 to 0.03:0.05, so a high emission cross-section maybe achieved at a relatively very lower content of YbF₃ than 1:3 that isthe ratio studied up to now.

FIG. 15A is an energy level diagram illustrating a photon emissionphenomenon according to absorption and downconversion of photons in anEr/Yb system and FIG. 15B is an energy level diagram illustrating aphoton emission phenomenon according to absorption and upconversion ofphotons in an Er/Yb system.

Downconversion is described first with reference to FIG. 15A. It can beseen that when Er/Yb are co-doped, operation is performed through threelaser energy levels (three level laser).

In this case, it can be seen that an energy transition phenomenon occursbetween ⁴I_(15/2) ⁴I_(11/2) transition of erbium (Er) and ²F_(7/2)²F_(5/2) transition of ytterbium (Yb) and a non-radiative transmissionphenomenon to ⁴I_(11/2) ⁴I_(13/2) of erbium (Er) is complexly shown,thereby influencing the carrier lifetime at ⁴I_(13/2).

When the concentration of ytterbium (Yb) increases, ²F_(7/2) ²F_(5/2)transition of ytterbium (Yb) and ⁴I_(15/2) ⁴I_(11/2) transition oferbium (Er) overlap, so an energy transfer phenomenon from ytterbium(Yb) to erbium (Er) increases. Further, as described above, the effectof ytterbium (Yb) ions reducing the non-radiative process of the erbium(Er) ions increases, so the carrier lifetime at the energy level of⁴I_(13/2) increases.

Next, upconversion is described.

Upconversion occurs in very (imitative situations and is almost notobserved in the natural world.

The upconversion phenomenon is a phenomenon of excitation to an energylevel higher than the energy of one photon due to not a single photon,but two or more photons. This is also called anti-Stokes-emission.

According to the upconversion phenomenon, an electron primarily isexcited to a high energy level by absorbing a photon and then it shouldabsorb another photon before dropping to the ground state. Accordingly,the electron primarily excited by absorbing a photon should exist at theprimarily excited energy level until it secondarily absorbs a photon.

Referring to FIG. 15B, as described above, some of carriers excited to⁴I_(11/2) through energy transition of ⁴I_(15/2)→2 ⁴I_(11/2) move to⁴I_(13/2) through non-radiative re-bonding and then move to ⁴I_(15/2)through radiative re-bonding.

Another carrier remaining at ⁴I_(11/2) is up-converted by anexited-state absorption phenomenon of excitation to ⁴F_(7/2) or ⁴F_(9/2)by another energy transfer of ⁴I_(15/2)→⁴I_(11/2).

The carriers up-converted to ⁴F_(7/2) or ⁴F_(9/2) drop to ²H_(11/2),⁴S_(3/2), and ⁴F_(9/2) through non-radiative re-bonding. The carriersdropped to ²H_(11/2), ⁴S_(3/2), and ⁴F_(9/2) drop again to ⁴I_(15/2) andre-bonding, thereby emitting photons of 523 nm and 545 nm and a photonof 651 nm.

FIG. 16 is a diagram illustrating a low-temperature upconversionemission spectrum of Al(PO₃)₃-(1−x)BaF₂—SrF₂-(0.03)ErF₃/(x)YbF₃-basedglass (x=0.05).

Referring to FIG. 16, a non-radiative attenuation ratio increases withan increase of temperature, so luminescence intensity decreases in ameasured entire wavelength region. However, intensity at a band of 521nm (²H_(11/2)→⁴I_(15/2)) increases. This phenomenon is because the YbF₃ratio and concentration increase due to thermal excitation of carriersfrom a level of ⁴S_(3/2) to a level of ²H_(11/2).

Accordingly, it can be seen that it is possible to analyze influence oftemperature on thermally coupled levels ofAl(PO₃)₃-(1−x)BaF₂—SrF₂-(0.03)ErF₃/(x)YbF₃-based glass through afluorescence temperature sensing method.

FIG. 17A is a diagram illustrating a fluorescence intensity ratio (FIB)of green emissions of Al(PO₃)₃-(1−x)BaF₂—SrF₂-(0.03)ErF₃/(x)YbF₃-basedglass (x=0.05) and FIG. 17B is a diagram illustrating a change accordingto temperature of sensitivity S.

The sensitivity S is a rate according to time of fluorescence intensityratio (FIR, hereafter, referred to as R).

Referring to FIG. 17A, it can be seen that, fluorophosphate glasses foran active device according to the present embodiment, the degree ofchange of the fluorescence intensity ratio (FIR) can be decomposed inaccordance with temperature even at cryogenic temperature (e.g., 100 Kor less).

Accordingly, as it can be seen from FIG. 17B, high sensitivity S isshown at cryogenic temperature.

S and maximum sensor sensitivity Tmax calculated on the basis of FIGS.17A to 17B are shown in Table 1.

Referring to Table 1, the fluorophosphate glasses for an active deviceaccording to the present embodiment (particularly,Al(PO₃)₃-(1−x)BaF₂—SrF₂-(0.03)ErF₃/(x)YbF₃ glass (x=0.05)) have S of22.4×10⁻⁴ and T_(max) of 123 K.

Accordingly, it can be seen that the fluorophosphate glasses for anactive device according to the present embodiment have high sensitivityS at cryogenic temperature (123 K) that has not been shown in any glassbase materials.

TABLE 1 Glass host Dopant S T_(max) T λ_(ex) Fluorophosphate Er/Yb 22123  10-300 980 Tellurite-zinc-niobium Er/Yb 95 363 276-363 980 Zincfluorophosphate Er 79 630 298-773 488 Fluorotellurite Er 79 541 100-573488 Tungsten-tellurite Er/Yb 28 690 300-745 980 Oxyfluoride glass Er 66570 293-720 488 Fluorophosphate Er/Yb 15 297  77-500 980 Glass ceramicEr/Yb 16 310 298-450 975 Silicate Er/Yb 33 296 296-723 978 FluoroindateEr/Yb 28 425 125-425 406

What is claimed is:
 1. Fluorophosphate glasses for an active device,comprising: a metaphosphate composition including Al(PO₃)₃; a fluoridecomposition including BaF₂ and SrF₂; and a dopant composed of ErF₃ andYbF₃.
 2. The fluorophosphate glasses of claim 1, wherein the YbF₃ isabout 3 mol % to about 5 mol %.
 3. The fluorophosphate glasses of claim2, wherein the ErF₃ is about 3 mol % and the YbF₃ is about 3 mol % toabout 5 mol %.
 4. The fluorophosphate glasses of claim 1, wherein theAl(PO₃)₃ is about 20 mol % to about 30 mol %, the BaF₂ is about 10 mol %to about 60 mol %, and the SrF₂ is about 10 mol % to about 70 mol %. 5.The fluorophosphate glasses of claim 4, wherein the Al(PO₃)₃ is about 20mol %, the BaF₂ is about 40 mol % to about 60 mol %, and the SrF₂ isabout 20 mol % to about 40 mol %.
 6. The fluorophosphate glasses ofclaim 5, wherein the ErF₃ is about 3 mol % and the YbF₃ is about 3 mol %to about 5 mol %.
 7. The fluorophosphate glasses of claim 4, wherein theAl(PO₃)₃ is about 20 mol %, the BaF₂ is about 60 mol %, and the SrF₂ isabout 20 mol %.
 8. The fluorophosphate glasses of claim 7, wherein theErF₃ is about 3 mol % and the YbF₃ is about 3 mol % to about 5 mol %. 9.The fluorophosphate glasses of claim 4, wherein the Al(PO₃)₃ is about 20mol %, the BaF₂ is about 50 mol %, and the SrF₂ is about 30 mol %. 10.The fluorophosphate glasses of claim 9, wherein the ErF₃ is about 3 mol% and the YbF₃ is about 3 mol % to about 5 mol %.
 11. Thefluorophosphate glasses of claim 4, wherein the Al(PO₃)₃ is about 20 mol%, the BaF₂ is about 40 mol %, and the SrF₂ is about 40 mol %.